As illustrated in FIG. 9(A), a carcass ply A of a pneumatic tire is formed using, as an original fabric, a long rubber-coated fabric d wherein a rattan blind woven stuff c obtained by weaving warps a and wefts b made of carcass cords into a rattan blind is coated with a topping rubber g.
Specifically, this rubber-coated fabric d is cut into plural cut pieces d1 at a desired angle θ (about 75 to 90° in a radial tire) to the side-edge of the fabric, and then ends de and de, on the side of the side-edge (on the non-cut side), of the respective cut pieces d1 are successively jointed (primary jointing j1), thereby forming a joint ply f wherein the carcass cords are arranged at the angle θ to the length direction.
As illustrated in FIG. 9(B), this joint ply f is cut into a constant length, which corresponds to one circumference, and the cut piece is wound on a drum along the circumferential direction and then both ends fe and fe thereof along the circumferential direction are jointed with each other (secondary jointing j2), thereby forming the cylindrical carcass ply A.
As illustrated in FIG. 10, in the primary jointing j1 and the secondary jointing j2, the so-called overlap joint is performed wherein the ends de and de, as well as the ends fe and fe, are overlapped with each other and jointed with each other under pressure. At this time, the joint portions j are formed to have a width jw, wherein four or more carcass cords overlap with each other in the vertical direction, in order to keep a necessary joint strength.
However, such an overlap joint has a problem that because of a large rigidity difference between the joint portions j and portions other than them the uniformity is lowered and damaged and further poor appearances called bulges and dents are caused.
In order to decrease the rigidity difference, it is desired that the joint portions j are made to have such a width that the number of overlapping carcass cords a is two or less. However, such joints have insufficient joint strength. Thus, when the carcass ply A is shaped, there arises a problem that the joint portions j are separated and opened. Thus, the manner has not been carried out.
In light of such situations, the present inventor made research. As a result, it has been made evident that the separation (opening) of the joint portions j is affected by the wefts b. That is, the wefts b are made of thin and weak organic fibers, and at the time of shaping the ply, the wefts are stretched in the circumferential direction to generate power in the direction along which the joint portions j are opened. In particular, the break elongation of conventional wefts is as larger as 60 to 150%; therefore, the wefts are elongated rather than cut. As a result, the power in the direction along which the joint portions j are opened is made larger.
The inventor has found out that in the case that the break elongation of the wefts b are restrained to 30% or less and the break strength thereof is restrained into 15 N or less, the wefts b are readily broken by tensile force at the time of the shaping; therefore, even if the number of the overlapping carcass cords a in the joint portions j is set to 2 or less, the joint portions j can be prevented from being separated (opened). At this time, the wefts b are preferably cut at a given pitch before the shaping. For this purpose, as illustrated in FIG. 11, it is preferred to pass the rubber-coated fabric d before primary jointing through a gap n between a pair of comb-teeth form roller r1 and r2 which engage with each other in a convex and concave manner, cause tension to act on the wefts b, and cut the wefts b. In the figure, symbol s represents a cut portion.
From further research by the inventor, it has also made clear that in order to make a further improvement in the uniformity, the cut pitch of the wefts b in side-edge areas E (shown in FIG. 9(A)) of the fabric d is made smaller than the cut pitch in a central area M between the side-edge areas E and E rather than the cut pitch of the wefts b is made constant (even) over the entire width of the fabric d. The reason for this is as follows. In the central area M, the carcass cords a slip out readily from the cut wefts b so as to be free. However, since the wefts b are folded into a lying U-shape in the side-edges of the fabric d, the carcass cords a get entangled to be restrained. As a result, at the time of the shaping of the carcass ply, intervals between the carcass cords are made coarse and minute, thereby producing a bad effect on the uniformity.
As the rattan blind woven stuff c, the following are well known: a woven stuff of a turn type, wherein a single weft b is made continuous; and a woven stuff of a tacking-in type, which is composed of plural tacking-in thread pieces ba wherein both ends of wefts b are terminated at folded portions b3 having a small length, as illustrated in FIG. 9 (A). However, in this tacking-in type woven stuff, the basal portion b1 of the tacking-in thread piece ba and the folded portion b3 overlap with each other so as to make an overlap portion in the side-edge area E. Therefore, in this manner, the strength against break is increased. Additionally, the power of restraining the carcass cords a is higher than that of the turn type. Accordingly, the tendency of the fall in the uniformity gets stronger.